Communication system



Aug. 2o, 1946.y

. A. c. scHRoEDER 2,406,165 -COMMUNICATION SYSTEM Filed July 1', 1944 HRUEDER Gttorneg Patented Aug. 20, 1946 UNITED STATES. PATENT oFFflfeE Alfredl C. Schroeder, ,Feasterville.Pa:assigner 1:0.1 RadiolCorporation. of America,f a; corporationpf Delaware Application July 1; 1944, seriallNo. 54311-761 11 claims. (01.179-15)vr This invention' relates-to-af communicationA systemtand particularly` to asystem of:` the type known@ as. an .f interoilice communication system. Inaprior.x art systems ofl this .type-which include a plurality of! stations; each; station L is ordinarily.

connectedj to. atleastlasiman-yv circui-ts as there arestationsf withfwhicli communication y is 1tobe effected... Installation and maintenance of such a system is,- accordingly, complicated andvexl'en` sive.-y

One-ofithe: objectsoft this; invention is to vprovide. an. improved communication-1 sys-temY using one interconnector betweennallithe stations;`

CIV

A-.furthenobiectiofthe invention iste provide K an improved communication system in which Another .objects-ofi' the invention is' toy provide# an.. improved? communicationE system wherein communication maya be eiected with a; plurality of stations-over: a common interccnnector.

Another object" ofan'iimproved`Y communication system includingy a nurnber ofl stations tems by! means-'1 of l anx interconnector common'U to all.` such stations-and? wherein asignalwillV be detectedv by the.. station= for Whic-h itL is--intended and by-no other-1 These. olii ect's-` are achieved -iniaccord'ance with .they-inventionbyA connecting"stati'ms"4 of theisystemsfiby .means `ofl 'a Asingle pulse-transmitting-l in' terconnector. and. by generating' synchronizing `pulsesf'-` in theinterconnector; eachstation includes means for appl-yingfto'the inteiconnector amplitude modulatedf signal pulses occurringduring.'l periods-in -th'ef intervals between" ltheA syn chronizing-l pulses.` These pulses differ" for each stationl to whichcommunicationiis Yto' be effected,` each station havingv assigned;A thereto aeportion of l the' time lin-terval between' recurring* synchronizing; pulses. Eachstation is# adaptedto detect modulated signal l pulsesf whichoccurduring .the peri'odassignedto it andduring no other period. Thisisfeiectedby providingeach station with adetector whichiis-able to detect modulatedsignal `pulses `.applied tolthe iinterconnect'or, but? which vis soribia'sed 1as'.to'give zero outputlexcept whenlenjergizedloy; aipulse-:from :a multivibratonalso provided@I ati. each?,` station.. This: multivibrator.. is

the invention is-A to f providev wherein communica-tion' mayLv be eiected between any two stations of the sys-A 23 i adapted to generate pulses onlyf'duringethefpe riod assignedto the stationiniwhich; itisa'ineluded, andthefdetector, therefore; detect's'fsignal pulsesoccurringfiduringithat periodi and-:no `other;`

The 'invention` may f be. better. understoodfromthe following more detailed.: description-thereof; wheny r'ead` in conjunctionv with the .ac'company-y f ing;v drawing in which:-

-Eigure 1-..is al-block diagram' offthesystemof thei invention,

Figure 2 visa-d'iagran'i illustrating: the'relation': to each. otherv in` time andiiamplitudez of?. theisynl-4 chronizing andsignal pulses before rr'ien-tionecl,`

Fig-urev 3 Sis Va .block-diagram .illustratingith'e re-I lation-to each other of'. the esscntiall elements:A of each station ini Iasystem according tothe-zins- Venti'on, and.

Figure .44s. a-b1ock diagram of each-station. in'v5 a preferred embodiment of the inventions.

The system comprises awnumlsierr of.` stations,`

and: by following the'fteachings of this specification, it. isr possible to-includeia in anyone'isystem. Inlordernotfto crowd the* drawing unduly.; only 8E of'thesef-stations'f are'- shown inFigv.' .1., a'i-iclthey.y arefnumberedr-leand All the stations-v arefconnected tolaesin'gle con-v centric'1ine',v coaxial cable l or other: pulse-trans@ mittingA circuitl2;havir1gl its= outery conductorv grounded; The systemf may betlri'oughtlof?asai chain; with sections-of -theline@connectingwad jacent." stations. Ea'ch.-v station will,y therefore;- have onlytw cables connected'ltoaitf-(apart-fromf connectionsV .to sources ofpower); onegoing toi the-preceding andlthe other tothe` succeeding station; The line iis-terminated" ati4 011e f endl BBF its characteristicl impedance 2li; anillconnectedv toits-other end in acpulse uniti-2163 which may include -a-\ multivibrator, amplifier and' av cl`1'ppljzr,` or other appropriate means) for applyingtothef line, andt therefore to f each" station, regularlyerecurring synchronizing pulses.vv Where the comir mu'nioation to vloe. effected' bythe systemis theV formv ofi speechl having a frequency-l not? in-V excess#- of 31,0001cyc1es-fper second; the pulses" may recur atl a f frequency of 6,000' cyclsperse'cond but'iifl greater de-lityfisdesired;l the repetitionl rateA` shouldfb'eI-increased.-

Figi' zfillustrates graphically two of these'syfnl" .chronizinglY pulses,-'- designatedv 2 Sit-25817, between-'f whichtherel isa time. interval. of"1/ sooo ofaisee#y on'df This interval is1dividedliito.portions7 each"L station offthe system beingfassigned'ftoioneyofA these'- portions. With L 20` stations@ in@ ail system;

least; 20Sstations.' f

Y station 3, for example,

' With the message to be sent, line 22,.` Y station of the line but, as explained, station 3 is phone 32,

' 22. :The otherl channel l to the, line22..

between recurring synchronizing pulses. Thus, station 3 is assigned to a portion of the interval which may be, but is not-necessarily, portion 3. This portion commences at time t after synchronizing pulse 28a and lasts for period 3. Similarly, station Il may be assigned to portion Il, which commences at time t' aftersynchronizing pulse 28a and lasts for period Il. If a message is .to be sent from any station of the system to there are generated at the sending station (in manner hereinafter explained) signal pulses 30, which occur during period 3 only. These signal pulses are amplitudemodulated at the sending stv tion, in accordance They are, therefore, received at every detect the only station of the system Which can these pulses. n pro-priate modifications apply to every other station Af ,theY system. 1

Referring now to Fig.` 3, it will be seen that at each station the line 22Vis connected to a clipper B, from the output of which' there are two pulse channels 34 and 36 in parallel. One channel 34 includes two'multivibrators D and F, the output of the latter multivibrator F being applied through a n Vor other modulating means, is also connected to this modulator, the output of the modulator being applied` by a conductor 38 or otherzpulse-transmitting channel back to the line 33 includes multivibratorsC and E, inv series, the output of the latter being applied to a grid electrode of a blocked detector G, YAnother gridelectrode of the detector Gr is connected by a similar conductor ,4B

The output of the detector is applied to la' speakerV 42. The multivibrator D is provided Vwith al number of keys 46. With 2O stations-on a line, each station will have 19 keys nurnberedto correspond with the numbers of each of the other stations These keysfare mechanically interconnected with the switch S3. Y

The tubes constituting the before-mentioned multivibrators, clipper, modulator and detector at each stationare al1 of well-known types and it isnot thought necessary to describe them or their associated circuits here in any detail. The only/special requirement for the blocked detector G and the modulator H is that they shall each have at least two grid electrodes. The clipper B maybe of the type described in U. S. Patent No. 2,132,655 to John l?.V Smith. The multivibrators may be of any appropriate type and in particular the multivibrator D may be of the ltype described in British Patent No. 456,840 to E. L. C. White.

The voperation of the system isas follows: Synchronizing pulses from the line 22 areapplied to the Vclipper B, which is so biased as to reject all pulses whose amplitude is below the clipping level shownln Fig. 2. This,V may be any conven- Vand-applied to the'V I Similar considerations with apl switch S3 toa modulator H. A micro-y seen that they occur at the saine frequency as the synchronizing pulses. Their amplitude is such that when fully modulated the clipping level shown in Fig. 2.

Pressing th'e key of multivibrator D at any station causes the mechanically interconnected switch S3 at that station to go from the normal (N) or open position Yto the call (C) or kclosed position. The signal pulses for multivibrator F are thus applied through switch S3 to the modulator H, where the pulses are modulated in accordance with the message from the microphone v32, and the modulated signal pulses Yare then applied through conductor 38 to the line 22.l

ient` level. The synchronizing pulses being in excess of that level are cut off by the clipper and the clippedtop portion of the pulses is employed to trigger multivibrator D, which sends out pulses commencing with the synchronizing pulses. The duration of these pulses depends on which key is pressed. If a message is to be sent to station 3,

'key 3 vWin be pressed. This win cause mumvi-Y brator Dto give pulses lasting time t. These pulses, lin turn, trigger multivibrator F, which sends gout pulses beginning at the/conclusion of time tand occurring during period 3. These are Y thesignal pulses before referred to, and it will be switches are Vmechanically interconnected with At this point, lit will be' observed that Vevery station in the system will receivevboth thesynchronizing pulses and the signal pulses from the sending station.V Since the signal pulses are ofV smaller amplitude than the clipping level,rthey will be rejected by clipper B and willy pass through conductor 40 to the detector G which is, how'- ever, so biased as :to have zero output except when l energized by a pulse from theemultivibratorE. On the other hand, synchronizing pulses `from the yline 22 are applied to and clipped by the clipper B. This, in turn, triggers multivibrator C which gives pulses lasting for a denite time, different for each station. In the case of station 3,

the pulses will last for time t, and inthe case of station Il they will last for time t'. The multivibrator E is triggered by the multivibrator .C

in the same way as the multivibrator Fis trig-y gered by the multivibrator D; that'is to say, it sends out a narrow pulse commencing at th'e conclusionV of the pulse from'the multivibrator C and lasting for the period assigned to thestation in which it is included. This pulse is used to energize the detector G so that Yin the example given,

the signal-pulses applied to the detector Gv from the line 22 and the energized pulses from the multivibrator E will coincide in time at station 3 only. The detector G then detects the signal and its output is applied to speaker 42.

In the form thus far described, the operator at station 3 (the receiving station) vwill hear the message transmitted, but will not know from what station he is being called until the sender tells him; and in orderv to reply, he will Lpress the key of the station from--which th'e signal Fig. 4 'is a block diagram of each station inthe system in a preferred embodiment of the'inven-Y tion. Each station will include all the elements described in connection with Fig. 3, rand, in addition thereto, a number of modications now described. A low-pass filter K, inserted between the microphone and the modulator H prevents modulation of the signal pulses by frequenciesY higher than half the pulse frequency, that is,

3,000 cycles per second, since such higher fre-` quencies will cause f undesired signals. Simi,-`

larly, a low-pass lter J, connected between theVV detector G and the speaker 42 prevents undesired frequencies higherY than half the pulse fref4 quency from reaching the speaker.

In the embodiment of Fig. ,4,- there 'arev seven switches in addition to the switch S3. All of these thekeys 46. A switch'Si connects the multivibrator E to the detector G; vS2 connects the filter J to the speaker 42; and Se connects the microphone 32 to the iilter K. The other switches will f be describedV inV connection withj'other elements they do not reach genoma? modulatorfH; throughE the call terminal'of/switch 4:0l`-

pendsomhestation atwhicuitisioted'. Thus, I'

ifa-'messagejis being set from station -3, the high frequency pulses vvillv be" turned 'ff three, times by three low fre'quency'pulses fromgthe call'keyjer Mi i Each vstationiis also providedwitha counter L' connected" to. a.' source j.' of power through the j normal contactfof "a switch vSiziand' to thefdetector G through the normal con-tact'of the switch-.52L e TheA counter is' provided With'a nuniber of'lights A corresponding to.` the;A number, of the other staf tions in; thefsystem. ."Itv `count'sthe 1 number `o`f times' the `signal vpulsesV from vthei sending. station ,A areJ turnedoff, by the' calllkeyer M andfs'witehes on thex light" which correspndsj toA the sending.

station. It ymay also bev adaptdjtoring abel-L or to. give such. other indication `as y.may bede? radio'j 'i1-li fIt'Lwil" lsoibefseenf thatA message lo f ultaneously between an sired. .Bythe addition f furtherrelaysfitmayalso be madevto operateautomaticallytheap propria/te key Illi-A o1- the m-ultivib11atorD, fso'thatf everything is in 1 readiness to nspeaky back' tof `tlre f. sending-station.

At the receiving station, also, the relayfRzf'is closed by theincomin'g call throughlaiswitch-Ss, connected'fbetween' 'iti-and the detectorijand 'this disconnects the'call keyer- M. ='-C1'osin`gi the relayv Rzfialso immediatelyiconneotsi-theimicrophone-S2f to athe modulatOrI-I-Ithiough th'eiltrfK 'softhat ff' to;speakbacktto the-f#seridi-ngsta'tionitl sary only for:Y th'efoperatoriatlthei'receiv toppressz .t1-rea key: of':multivibraton(D:correspontungi75 y f f pairs-ofstationsoftheesystem'f4` f ai L thusabeenedescribed'lancommuniaz" tion-2 system tions Having assigneditnereto aspjrtdetemanned each 'fJsaidf stations, anni-'means atjfeach 'stat-ionJv for-J apply-ingeto ff said circuit' 'modulated i -si'gnai-" pulses iand fors'seleetinrg a-period for ythej occu' "l cuitlu e occurringd-uringea predetermined ipe-f riodf y; sa-id period "having afp r'edetermir'red i titne-'relation^ to l-safid isyncl'iro'nizin'g pulses *fand* v said relation being diiierent for each of said stationsy'andl means ateachl A*station for apJlSng to said circuitfr modulated signal Apulses capabiefof" being detected by another f of said 1stations-'Jayv afc' resaid,` 'and-for selecting 'thefperiodi during" Whio'h'lsaid fsignal pulses#v occur;V l l v4:. Af communication `systemfincludingaidui ralityofistatons; cables 'connected "to each fof'isaid f lstations andfconneoting;'sai'd-fstation to; the pre-v ced-ing v and* succeeding stations v respectively; mea-ns Afor"fapplyi-rig regularlyfrecurring*synehror nizingplses to? the circuit' constitutedb'yjsafd* stations -aridsaid` 'Ycables; each'` f saidstations be'- f in'g adapted to- `detectfmodulatedfsignal plses'lap'- pliedfto.y saidv circuitian'd occurring duringfafspre-l det'erminedlperiodonly, said period having'f'aV predetermined -1 time# relation! tosaid fsynchronlizr` ingtpulsesianu said-relation beingfdmerentifor-2 pulses "during-l 3 acteristic impedance, a

for applying toV Vsaid circuit .modulated 'signal1 being detected by another ofc pulses capablek of saidlstations Yas aforesaid,gand for selecting the period Nduringwhich said signal pulses occur.

V5, A communication system including a pluralityV of stationsa single coaxial cable connecting said stations and terminated. at one end thereof b'yits characteristic impedance, a pulse ,unitconnected to said cable at its other end for applying regularly recurring Y synchronizing pulses -to said cable,' ieacl 1 ofsaid stations beingV adapted. toA

detect modulated signalv p ulses applied to said vcable land occurring during a predetermined-pee Vriod only,` said period having a predetermined time?,V relation to said Ysynchronizing pulses and said relation being different foreachY of said stations, and meansat eachstation for applying to saidcablemdulated signal pulses capable of be-,-

in gv'dete'cted by another of said stationsI as arbre-1 said, and for selecting the period' during: said* signal pulsesV occur.

which Y6.1A communication system including a 'plurality of stations, a single pulse-transmitting circuit A.connecting said stations, means for applying regularly-recurring synchronizing pulses to said circuit, each of said stations including a multivibrator and a detector, said multivibrator being adapted to apply to said detector energizing pulses occurring riod' ,only,said 'periodA having a; predetermined time relation tovsa1d synchronizing, pulses, and

said'relation being different'vfor each of said stabeing adapted to detect Y tions, and said detector modulated signal. pulses applied thereto through said. circuit; on being: energized by said multivibrator asaforesaid, and means at each, station for applying to said circuit modulatedY signalpulses capable f being during which -*said signal pulsesoccur. Y '77. v-A" communicatiom system including av plurality of stations, a pulsetransmitting circuit connecting said stations, means for applying regularly-recurring synchronizing pulses to saidcircuit, eachk of said stations being adapted to detec't modulated signal pulses applied to said circuit and oecuringduring a predetermined period' only,l said period having a predetermined time detected. by another of said stal tions as aforesaid, and for selecting the period during y at predetermined perelation-,to said synchronizing pulses and said Y relation being different foreach of said stations,

means at each station including a key-controlled multivibrator activated 'by said synchronizing Vpulses for applying to saidcircuit modulated sigy y detected by another Y of saidstations as aforesaid, and means for` se nal` pulses capable of Ybein lecting the periodduring lwhich said signal pulses occur. Y

QA'communication circuit including a plurality of stations, a plurality of sections of a coaxial cable, each of said sections connecting one of saidstations to the next succeeding station, said cable being terminated thereto 011 being aiivaiediby saidzlastmentoned relation being different andfsaiddetector being adapted ,to detect modulated signal muses applied:

multivibrator, as aforesaid, and means at each stationincluding amodulator and akey-con-i trolled multivibratoradapted to be activatedrby said synchronizing pulses; for .applying to said circuit modulated signal pulsesv capable of being detected by, another of said andfor selecting thev period duringv which said signal pulses occur.'

SLfAV communicationpsystem including a single,

pulse-transmitting Y circuit, a plurality -ofstations eectively connected at points on said circuit,Y

means forapplying to said circuit regularly-recurringsynchronizing pulses, each of said stations having assigned thereto a predetermined period in the ,intervals between said pulses,gs aid f period having-a predetermined time relation to` Y l relation being different .forwf each station of the system, means at each station.. for generating signal pulses, for., selectinglperiods z said pulses, and said forthe-occurrence of said. pulses corresponding to the periods assigned to the; other stations of the system, for modulating said signal pulses and for applying said signal pulses to said circuit,

each of said stations including at least two chan-` nels, means at each station for diverting synchronizing pulses applied thereto to one of said channels and signal pulses applied thereto to an- I other of said channels, and means in the second ofv said channels for. detecting signal pulses divertedtheretoand occurring during the period assigned to the station in which said detecting means are located, Y

10. A communication system including a single pulse-transmitting circuit, `a plurality of Ystations effectively means for applying to said circuit regularly-recui-ring synchronizing pulses having an amplitude in excess of a predetermined level, each of Y said stations having assigned thereto a prede-iY termined period inthe intervals between said pulses, said period having a predetermined time relation to said pulses and said relation being diiferent for each station of of said stations including (a) a clipper for clipping said pulses at said level and adapted to be activated by pulses having an amplitude in excessl of said-level, (b) means-including at least one multivibrator adapted to be activated by said Y clipped pulses for generating signal pulses having the amount an amplitude,Y less than said level by of a predetermined amplitude of the modulation, (c),l means controlled by keys associated with said multivibrator for 'selectingperiods for the occurrence of said Y periods assigned to the other stations of the sys-,1 tem, (d) means circuit, (e) means including' at least another multi-vibrator adapted to .be activated by said clipped pulses forV generating activating pulses occurring' onlyduring the period assigned to theY station in which such means are located, and (f)4 means including a detector adaptedto be activated by said activating pulses only for detecting modulated signal pulses applied to said circuit and occurring 'during the period assigned to said station.

1l. The method of Aeffecting communication between va4 plurality of stations effectively connected rto points, on 'a single pulse-transmitting circuit, including-,the following steps: y(1) Grenv erating Vrinsaid circuit regularly-recurring synchronizingpulses,V `(2) Adjusting eachstation of. thesystemtoa predetermined period in the in-Vv I1 tevgglvals between said pulses'. fsaidperiod bearing a stations as aforesaid,

connectedat points on said circuit, and

the system, each l signal pulses corresponding to the i for modulating Vsaid signal pulses andfor applying saidmodulated pulses to said' a predetermined time relation to said pulses and said relation being different for each of said stations, (3) Generating signal pulses at one station, (4) Selecting a period for the occurrence of said signalvpulses corresponding to the period 5 assigned to a responding station, (5) Modulating said signal pulses in amplitude in accordance with the communication to be effected, (6) Ap- 10 plying said modulated pulses to said circuit, (7) Diverting synchronizing and signal pulses applied to said responding station into separate channels, (8) Detecting signal pulses diverted to one of said channels and occurring during the period assigned to the responding station.

ALFRED C. SCHROEDER.

Disclaimer 2,406,165.-A7fmd O-''chroede, Feasteville, Psi; COMMUNICATION SYs'IEM-Q Patent dated Aug.' A20, 1946. Disclaimer filed Oct. 29, 1948, by the assignee, Radio Corpora/tion Of America. Hereby enters this disclaimer to claims 1, 3, 4, and 9 of said patent.

[Ocal Gazette Dec. 7, 1948.] 

